1. Field of the Invention
The present invention relates to a dental mixing pad that is used as a substrate in mixing and kneading a dental material such as a dental cement or a resin-based material, using for dental adhesives or dental filling-materials, on its mixing surface in the dental remedy. Particularly, the present invention relates to a dental mixing pad suitable for mixing and kneading a dental material such as the photopolymerization type dental cement.
2. Description of the Related Art
Hitherto, glass slab were employed as a mixing pad in mixing and kneading a dental material such as a dental cement or a resin-based material, using for dental adhesives or dental filling materials. However, they are liable to be broken, or are troublesome because they must be cleaned every time in use. Thus, in recent years, there have been used disposal mixing pads made of paper, synthetic paper, plastic film, plastic-coated paper, or the like.
For these disposable mixing pads, in order that a component to be mixed and kneaded (such as a cement powder or a cement liquid) does not penetrate or does not cause unnecessary chemical changes, or that a mixed material is easily taken out from its mixing surface, a paper having mixing surface coated with a plastic such as polypropylene or polyethylene, or a polypropylene film, a polyethylene film or the like, are used. In these mixing pads, the color to be used in the mixing surface side was generally white.
On the other hand, recently, photopolymerization type dental material such as a dental cement, a resin-based material, or the like and having a photopolymerization catalyst added thereto have become popularized. These dental materials are used for a desired purpose by filling in an oral cavity, etc. and then subjecting to polymerization and hardening through irradiation with a light. As described above, since the photopolymerization type dental material have such a characteristic that the reaction rapidly proceeds upon irradiation with a light, they involve a problem that the polymerization reaction proceeds even with a illumination of a circumferential light such as a shadowless lamp, a room lamp or sunlight in the circumference of remedy works, whereby the working time becomes short. Actually, there were problems that, in a case of a disease where it takes a time for filling operations, or in a case where after a dental hygienist has mixed a dental material on a mixing pad, for some reason, it takes a time for a dentist to use it, the photopolymerization reaction of the photopolymerization type dental material proceeds too much on the mixing surface, whereby the working time is lost, and that depending on circumstances, the photopolymerization type dental material is hardened before use, so that it is no longer useful, whereby the measuring and mixing and kneading operations of the dental material must be carried out again.
The present invention is aimed to provide a dental mixing pad which can decrease a polymerization reaction of a photopolymerization type dental materials which is caused by a illumination of circumferential lights to proceed too much, without using excessive operations or a special device, while overcoming the defects accompanied with the current dental mixing pad, for example, where the above-described current photopolymerization dental materials are used, decrease in working time, hardening of the material, due to the polymerization reaction with a illumination of circumferential lights.
In order to achieve the above-described aim, the present inventors made extensive and intensive investigations. As a result, they paid attention to that usually, in a photopolymerization type dental material, not only the polymerization from a surface of a mixed material occurs by direct lights, but also the polymerization is further accelerated by reflected lights on the surface of the dental mixing pad. Then, it has been found that when a mixing surface side of the dental mixing pad is constituted by a color having a low reflectance of a light having a wavelength of 470 nmxc2x180 nm, at which a photopolymerization catalyst is excited, an excessive polymerization reaction of the photopolymerization type dental material by reflection from the surface of the dental mixing pad can be greatly suppressed and that the working time of the photopolymerization type dental material can be readily ensured, leading to the accomplishment of the present invention.
Further, it has been found that: it is preferred that the color having a low reflectance of a light having a wavelength of 470 nmxc2x180 nm, which constitutes the mixing surface side of the dental mixing pad, is satisfied with at least one of the following requirements: that is, in a standard illuminant D65, L* is 80 or less, and C* is less than 20; L* is 80 or less, and h is 50xc2x0xc2x180xc2x0 (i.e., from 0xc2x0 to 130xc2x0 and from 330xc2x0 to 360xc2x0); and L* is 30 or less, when expressed by an L*C*h color space.
The dental mixing pad according to the present invention is described below in detail.
An excitation wavelength to be used for polymerization with visible lights in photopolymerization catalysts that are generally used as a photopolymerization type dental material is generally 470 nmxc2x180 nm. For this reason, when the dental mixing pad is colored into a color where, among lights to be reflected from a mixing surface of the dental mixing pad, a light having a wavelength of 470 nmxc2x180 nm has a light reflectance of 60% or less, and preferably 40% or less, a decrease in the working time can be remarkably suppressed.
The light having a wavelength of 470 nmxc2x180 nm includes colors of a violet color (397 nm), an indigo color (431 nm), a deep blue color (486 nm), and a green color (527 nm) in terms of luminance spectrum. For this reason, when a mixing surface side of the mixing pad is constituted by a color having a low reflectance of a light having such a wavelength, the polymerization reaction caused by the reflection from the surface of the dental mixing pad of the photopolymerization type dental material can be readily suppressed, without applying excessive operations or using a special device. Specifically, suitable examples of the color that can lower the reflectance of a light having a wavelength of 470 nmxc2x180 nm include a color having a low lightness and a low chroma (i.e. a low reflectance of the whole of visible lights) or a color having a low lightness and a long wavelength, inclusive of a yellow color (589nm), an orange color (636 nm), a crimson color (687 nm), and a deep red color (759 nm). When the mixing surface side of the dental mixing pad is constituted by such colors, the reflectance of a light having a wavelength of 470 nmxc2x180 nm, at which the photopolymerization catalyst is excited, can be controlled to 60% or less.
The color having a low reflectance of a light having a wavelength of 470 nmxc2x180 nm is a color that is satisfied with at least one of the following requirements: that is, in a standard illuminant D65, L* is 80 or less, and C* is less than 20; L* is 80 or less, and h is 50xc2x0xc2x180xc2x0; and L* is 30 or less, when expressed by an L*C*h color space. Incidentally, in the L*C*h color space, L* expresses a lightness of the color, C* expresses a chroma, and h is an index expressing a hue. When this color space is expressed in terms of an L*a*b* color specification as defined in JIS Z8729, xe2x80x9cSpecification of Colour of Materials according to the CIE1976 (L*a*b*) space and the CIE1976 (L*u*v*) Spacexe2x80x9d, L*=L*, C*={(a*)2+(b*)2}xc2xd, and h=tanxe2x88x92l (b*/a*) .
In the L*C*h color space, the lightness is expressed by a numeral value L* of from0to 100, in which L*=O means jet-black, and L*=100 means pure white. The higher or the lower the L* value, the less the influences of the hue or chroma are. In particular, in case where L* is higher than 80, the reflectance of all of the hues is high, and an effect for suppressing the polymerization reaction by a illumination of circumferential lights is low. Accordingly, it is preferred that L* is 80 or less.
In the L*C*h color space, C* represents a chroma and is expressed by numerical values of from 0 to 60. C* expresses a distance from the center point, crossing the a* and b* ordinates in the L*C*h color space. The smaller the C* value (the nearer to the center point), the lower the chroma is. In case where L* is 80 or less, and C* is less than 20, the reflectance of the light rays is low regardless of the h value as described below, thereby obtaining an effect for suppressing the polymerization reaction with a illumination of circumferential lights.
In the L*C*h color space, h represents a hue and is expressed by angles of from 0xc2x0 to 360xc2x0. The h value represents an angle for the movement against a hue in the counterclockwise direction based on a coordinate in the red direction (+direction) of the a* coordinate in the L*C*h color space as defined to be 0. So far as the mixing surface of the dental mixing pad according to the present invention is constituted by a color having the L*=80 or less and a low reflectance of a light having a wavelength of 470 nmxc2x180 nm inclusive of a yellow color (h=130xc2x0), an orange color (h=50xc2x0), and a deep red color (h=330xc2x0), i.e., within a range of 50xc2x0xc2x180xc2x0, there gives rise to an effect for suppressing the polymerization reaction with a illumination of circumferential lights, regardless of the C* value.
Incidentally, in case where L* is 30 or less, the color becomes close to a black color, the reflectance of a light having a wavelength of 470nmxc2x180nm can further be suppressed, regardless of the C*h values.
As for the photopolymerization catalyst to be used for the photopolymerization type dental material, a UV absorber may be applied simultaneously with the coloration, thereby improving an effect against the whole of a illumination of circumferential lights inclusive of a ultraviolet, etc. In this case, a degradation with a lapse of time of the dental mixing pad can also be prevented. Further, a coating having a matting effect may be used in combination.
As a raw material to be used for the dental mixing pad according to the present invention, those used for the current dental mixing pad and mixing substrates, such as plastic films, plastic-coated papers, and synthetic papers, can be used. For instance, the dental mixing pad according to the present invention is supplied in a filing state in which on a board composed of a square cardboard having a length of side of about 50 mm are stuck from about 20 to 100 sheets of a polypropylene-coated paper having the same size as in the board.